The present invention relates to a sheet feeding apparatus with a cross-cutter in front and, following the cross-cutter, a device for forming a series of overlapping sheets with lifting and holding elements located in the region between two withdrawal devices driven at different feed speed; these elements lift the rear edge of each sheet to form a lead-in gap for the following sheet.
An arrangement of this type is known from German Patent 20 10 467. With the known arrangement, to form the lift and holding elements, reciprocating suction groups are used which are arranged so that the one group is placed in the starting position while the other group is preferably dragged by the sheet itself into the sheet run direction. These suction groups may be suspended like a pendulum on a common axis. An arrangement of this type is relatively simple and with low operating speeds has led to useful results. However, for increased speeds, this arrangement was found too slow. Because of the high sheet there is the danger that the sheet grabbed by one suction group slips off the suction (cups) or is pulled off so that the lead-in gap for the following sheet becomes lost.
This could be counteracted by an outside drive of the unit formed by the suction groups. However, such a drive would be extremely difficult and unduly expensive since the reciprocating suction groups must be moved at constant speed throughout their entire operating range and must be greatly retarded and accelerated in the region of each reversal point. A drive meeting these requirements requires considerable expenditure. In addition, the mass (inertial) forces act unfavorably. The aforementioned German Patent No. 20 10 467 also mentions suction rollers. To guarantee a sufficiently long holding travel (path), large roller diameters would have to be used which would lead to excessive space requirement. Also, the large size would result in increased material and manufacturing costs.
An attempt has been made to increase the limited operating speed by placing a periodically actuated striking flap for lifting the sheets. This would avoid suction devices and the related construction cost and time, but would not remove the disadvantages of discontinuous operation.
It is, therefore, the object of the present invention to avoid the disadvantages of the known arrangements and to provide with small expense an arrangement of the above type which even with increased speeds guarantees a high functioning reliability and a careful operation and still saves space.
Another object of the present invention is to provide an arrangement of the foregoing character which may be readily maintained in service and may be economically fabricated.
A further object of the present invention is to provide an arrangement, as described, which has a substantially long operating life.